The present invention relates to a modified polyimide resin which is useful in imparting reduced shrinkage upon setting to a thermosetting resin composition and also useful in imparting heat resistance and pliability and the like to a hardened article of such thermosetting resin composition (hardened resin), and to a thermosetting resin composition containing the same, as well as to a film carrier comprising a surface protection film formed by coating an overcoat agent containing such composition as the main component followed by setting it, and to a carrier device employing such film carrier.
The surface protection films of flexible wiring circuits have heretofore been produced, e,g., by a method in which a polyimide film called a coverlay film is punched with a metal template having a certain pattern and then bound with an adhesive or a method in which an overcoat agent containing as the main component a UV setting resin imparted with a flexibility or a thermosetting resin is applied by a screen printing and then allowed to set. However, since a coverlay film method has a disadvantage in terms of an processability and a method employing an overcoat agent involves a problematic warping upon setting as well as a poor pliability of a hardened resin, there is still no method for forming a surface protective film for a flexible wiring circuit substrate whose performance satisfies all requirements.
On the other hand, the so-called TAB method employing a film carrier suitable in imparting a higher density and a less thickness to a liquid crystal-driving IC package, has got increasingly employed recently. A basic structure of a film carrier is mainly composed of a heat-resistant, insulating film substrate, such as one made from a polyimide, and an electrical conductor such as copper foil, bound thereto via an adhesive whose main component is an epoxy-based resin, the wiring pattern having been formed on the copper foil by etching. Afilm carrier device is made by connecting an IC to a film carrier (referred to also as a tape carrier) followed by confining with the use of a confining resin, and the film carrier is generally covered with a surface protecting film from an overcoat agent for the purpose of preventing reduction in reliability due to the occurrence of a pattern short, erosion, migration, whiskering and the like during the step before connecting an IC. While an overcoat agent employed for a film carrier has been an epoxy-based one or a polyimide-based one, the former has not been satisfactory because of warping upon setting and a poor pliability of the resultant film, and the latter has not been satisfactory in terms of adherence to an IC confining resin and a processability, resulting in the fact that two or more overcoat agent have been employed to compensate each other for their shortages (JP-A 6-283575).
Under the circumstance of the prior art described above, an object of the present invention is to provide a resin composition capable of fully satisfying the requirements with regard to the characteristics of an overcoat agent for a wiring circuit which should be pliable, such as a flexible wiring circuit substrate and a film carrier.
We have made an effort to solve the problems described above, and finally discovered that a modified polyimide resin having a polybutadiene skeleton represented by Formula (4) shown below is extremely useful as a component of an overcoat agent for a flexible wiring circuit substrate and a film carrier, more specifically, that a thermosetting resin composition obtained by mixing a polybutadiene polyol having a number average molecular weight of 1,000 to 8,000 and 2 to 10 hydroxyl groups per molecule (Component A), a modified polyimide resin represented by Formula (4) shown below (Component B) and a polybutadiene polyblock isocyanate having a number average molecular weight of 1,000 to 8,000 and 2 to 10 hydroxyl groups per molecule (Component C) at a certain ratio, can serve as a resin composition for an overcoat which has a performance capable of satisfying the requirements with regard to various characteristics, including reduced shrinkage upon setting, and pliability, tight adherence, electric insulation, chemical resistance and heat resistance of a hardened article, thus establishing the present invention. 
wherein R1 represents the residue obtainable by removing all the carboxyl groups from an organic compound having 4 carboxyl groups (tetrabasic acid), R2 represents the residue obtainable by removing all the isocyanate groups from an organic compound having 2 isocyanate groups, and R3 represents the residue obtainable by removing the hydroxyl group from a hydroxyl-terminal polybutadiene; L2 and M2 represent the ratio of the number the component polybutadiene units and the ratio of the number of the component polyimide units, respectively, to the total number of both the kinds of units and n3 represents a degree of polymerization, provided that L2+M2=1,0 less than L2 less than 1,0 less than M2 less than 1 and 1xe2x89xa6n3xe2x89xa61,000 simultaneously.
Accordingly, the present invention relates, firstly, to a modified polyimide resin obtainable by reacting the following three (3) kinds of compounds, i.e., a bifunctional hydroxyl-terminal polybutadiene having a number average molecular weight of 800 to 5,000 (Compound a), a tetrabasic acid dianhydride represented by Formula (1) (Compound b): 
wherein
R1 represents the residue obtainable by removing all the carboxyl groups from an organic compound having 4 carboxyl groups, and a diisocyanate compound (Compound c), said modified polyimide resin being represented by Formula (2): 
wherein
R1 represents the residue obtainable by removing all the carboxyl groups from an organic compound having 4 carboxyl groups, R2 represents the residue obtainable by removing all the isocyanate groups from an organic compound having 2 isocyanate groups, and R3 represents the residue obtainable by removing the hydroxyl group from a hydroxyl-terminal polybutadiene; L1 and M1 represent the ratio of the number of the component polybutadiene units and the ratio of the number of the component polyimide units, respectively, to the total number of both the kinds of units and n1 represents a degree of polymerization, provided that L1+M1=1,0 less than L1 less than 1,0 less than M1 less than 1 and 1xe2x89xa6n1xe2x89xa610,000 simultaneously.
The present invention relates also to various modified polyimide resins obtainable by specifying inter alia amounts of the starting materials for their synthesis. There may be mentioned as such modified polyimide resins, e.g., a first modified polyimide resin represented by Formula (2) shown above, and obtainable by reaction between an isocyanate group-containing product (Starting material 1, isocyanate equivalent number:X equivalent(s)) which can be obtained by reacting a bifunctional hydroxyl-terminal polybutadiene having a number average molecular weight of 800 to 5,000 (Compound a) with a diisocyanate compound (Compound c) at a hydroxyl groups:isocyanate groups ratio of 1:1.5 to 2.5 in terms of equivalent number, and a tetrabasic acid dianhydride represented by Formula (1) shown above (Starting material 2, acid anhydride equivalent number: Y equivalent(s)), the isocyanate-group containing product being represented by Formula (3): 
wherein
R2 represents the residue obtainable by removing all the isocyanate groups from an organic compound having 2 isocyanate groups, and R3 represents the residue obtainable by removing the hydroxyl group from a hydroxyl-terminal polybutadiene; n2 represents a degree of polymerization, provided that 0xe2x89xa6n2xe2x89xa6100; a second modified polyimide resin represented by Formula (4) shown above and obtainable by reaction between Starting materials 1 and 2 in amounts in terms of equivalent numbers satisfying Y greater than Xxe2x89xa7Y/3,0 less than X and 0 less than Y simultaneously in the above reaction; a third modified polyimide resin represented by Formula (2) shown above, and obtainable by reacting a modified polyimide resin represented by Formula (4) shown above, further with an isocyanate group-containing product represented by Formula (3) shown above and/or a diisocyanate compound described above (Starting material 3, isocyanate equivalent number: Z equivalent(s)); and a fourth modified polyimide resin represented by Formula (4), and obtainable by reacting Starting materials 1, 2 and 3 in amounts in terms of equivalent numbers satisfying Yxe2x89xa7(X+Z)xe2x89xa7Y/3, 0.2xe2x89xa6(Z/X)xe2x89xa65,0 less than X, 0 less than Y and 0xe2x89xa6Z simultaneously.
The present invention relates, thirdly, to an insulating resin composition for overcoat of flexible circuits comprising, as the essential component, the following three kinds of components, i.e., a polybutadiene polyol having a number average molecular weight of 1,000 to 8,000 and having 2 to 10 hydroxyl groups per molecule (Component A), a modified polyimide resin described above (Component B) and a polybutadiene polyblock isocyanate having a number average molecular weight of 1,000 to 8,000 and having 2 to 10 block isocyanate groups per molecule (Component C), wherein the weight ratio of Component A and Component B is a (A):(B) ratio of 40:60 to 90:10 in terms of solid matter, and also wherein the amount in terms of equivalent number of the polyblock isocyanate is 0.8 to 3.5 times the sum of the hydroxyl group equivalent number of Component A and the acid anhydride equivalent number of Component B.
The present invention relates, finally, to a film carrier comprising an insulating film and a pattern formed thereon of metal thin film, with a part or all of the insulating film in the folded region having been removed, wherein the circuit pattern side except the joint region including the folded region, is coated with an overcoat composition whose main component is the resin composition as described above, and a film carrier device employing the film carrier as described above.
The present invention will be described below in greater detail.
The modified polyimide resin of the present invention means mainly those modified polyimide resins represented by Formula (2) shown above, and obtainable by reacting the following three kinds of compounds, i.e., a bifunctional hydroxyl-terminal polybutadiene having a number average molecular weight of 800 to 5,000 (Compound a), a tetrabasic acid dianhydride (Compound b) represented by Formula (1) shown above, and a diisocyanate compound (Compound c).
For the polyimide units to be efficiently incorporated into the resin, they are preferably synthesized as follows. That is, a modified polyimide resin represented by Formula (2) shown above can be obtained by reacting a bifunctional hydroxyl-terminal polybutadiene having a number average molecular weight of 800 to 5,000 (Compound a) with a diisocyanate compound (Compound c) at a hydroxyl groups:isocyanate groups ratio of 1:1.5 to 2.5 in terms of equivalent number, to obtain an isocyanate group-containing product represented by Formula (3) shown above (isocyanate equivalent number:X equivalent(s)) followed by reacting the isocyanate group-containing product with a tetrabasic acid dianhydride represented by Formula (1) shown above (Compound b, acid anhydride equivalent number: Y equivalent(s)). Alternatively, a compound represented by Formula (3) and a compound represented by Formula (1) (Compound b) are reacted with each other in amounts in terms of equivalent numbers satisfying Y greater than Xxe2x89xa7Y/3,0 less than X and 0 less than Y simultaneously, in the above reaction, to obtain a modified polyimide resin represented by Formula (4), which resin is then reacted with an isocyanate group-containing product represented by Formula (3) shown above and/or a diisocyanate compound described above (Starting material 3,isocyanate equivalent number: Z equivalent(s)), whereby a modified polyimide resin represented by Formula (2) can be obtained. Incidentally, the equivalent number of an isocyanate to be reacted with a modified polyimide resin represented by Formula (4) is expressed as Z, which represents a total equivalent number when only one of or both of an isocyanate group-containing product represented by Formula (3) and a diisocyanate compound (Compound c) are employed. Unless an attention is paid to the reaction conditions as described above, side reactions such as a reaction between an acid anhydride group and a hydroxyl group or a reaction between isocyanates may occur, or a reaction between an isocyanate group and an acid anhydride group may be predominant, resulting in precipitation of polyimide unit(s) only, which may lead to difficulties in integrating a polyimide unit into a resin backbone efficiently, thus resulting in a possibility that a resin having excellent mechanical properties and hydrolysis resistance is not obtained.
Furthermore, a high-molecular compound having too a large molecular weight generally has a higher viscosity of a resin solution, because of which it becomes to involve difficulties in being used as a resin composition such as an overcoat agent. Accordingly, it is preferable to vary the ratio of the starting materials for a resin appropriately to avoid an excessive increase in the molecular weight. Thus, an isocyanate group-containing product represented by Formula (3) (Starting material 1, isocyanate equivalent number: X equivalent(s)) and a tetrabasic acid dianhydride represented by Formula (1) (Starting material 2, acid anhydride equivalent number: Y equivalent(s)) are charged into a reactor in amounts in terms of equivalent numbers preferably within a range of the equivalent numbers satisfying Y greater than Xxe2x89xa7Y/3. When they are reacted further with an isocyanate group-containing product represented by Formula (3) and/or a diisocyanate compound described above (Starting material 3, isocyanate equivalent number: Z equivalent(s)), the amounts in terms of equivalent numbers, of Starting materials 1, 2 and 3 should satisfy the relationship of the equivalent numbers represented by Y greater than (X+Z)xe2x89xa7Y/3 and 0.2xe2x89xa6(Z/X)xe2x89xa65. In case of Y less than X or Y less than (X+Z), polymerization is effected in an isocyanate group-excessive system, which allows side reactions to take place readily and leads to a difficulty in controlling the reaction, while in case of X less than Y/3 or (X+Z) less than Y/3, an acid anhydride is present in a large excess, due to which a molecular weight sufficient to exert a performance can not be obtained. In case of 0.2 greater than (Z/X), a flexible butadiene backbone is present in a large proportion, which yields a highly pliable resin but results in an insufficient heat resistance at the same time, while in case of (Z greater than X) greater than 5, a polyimide backbone is present in a large proportion, which leads to a poor solubility in a solvent, resulting in a higher viscosity of the solution and precipitation of the imide component, which leads to a difficulty in handling.
The bifunctional polybutadiene having a number average molecular weight of 800 to 5,000 to be employed in the synthesis of an isocyanate group-containing product represented by Formula (3) which is Starting material 1 for modified polyimide resins according to the present invention, includes those whose unsaturated bonds have been hydrogenated, and can for example be, but are not limited to, xe2x80x9cG-1000xe2x80x9d, xe2x80x9cG-3000xe2x80x9d, xe2x80x9cGI-1000xe2x80x9d, and xe2x80x9cGI-3000xe2x80x9d (all produced by NIPPON SODA) and xe2x80x9cR-45EPIxe2x80x9d (produced by IDEMITSU PETROCHEMICAL).
The diisocyanate to be employed in the synthesis of an isocyanate group-containing product represented by Formula (3) which is Starting material 1 for modified polyimide resins according to the present invention, includes, but is not limited to, toluene-2,4-diisocyanate, toluene-2,6-diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, diphenylmethane diisocyanate, isophoronediisocyanate and the like.
The tetrabasic acid dianhydride represented by Formula (1) (Compound b) to be employed as Starting material 2 for modified polyimide resins according to the present invention can for example be, but is not limited to, pyromellitic dianhydride, benzophenonetetracarboxylic dianhydride, biphenyltetracarboxylic dianhydride, naphthalene tetracarboxylic dianhydride, 5-(2,5-dioxotetrahydrofuryl)-3-methyl-cyclohexene-1,2-dicarboxylic anhydride, 3,3xe2x80x2-4,4xe2x80x2-diphenylsulfonetetracarboxylic dianhydride, 1,3, 3a, 4,5,9b-hexahydro-5-(tetrahydro-2,5-dioxo-3-furanyl)-naphtho[1,2-C]furane-1, 3-dione and the like.
The diisocyanate compound (Compound c) described above to be used as Starting material 3 for modified polyimide resins according to the present invention can for example be, but is not limited to, toluene-2,4-diisocyanate, toluene-2,6-diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, diphenylmethane diisocyanate, isophorone diisocyanate and the like.
The modified polyimide resin of the present invention can be obtained by reacting the three (3) kinds of compounds, i.e., a bifunctional hydroxyl-terminal polybutadiene having a number average molecular weight of 800 to 5,000 (Compound a), a tetrabasic acid dianhydride (Compound b) and a diisocyanate compound (Compound c), and, in a preferred procedure, a bifunctional hydroxyl-terminal polybutadiene having a number average molecular weight of 800 to 5,000 (Compound a) and a diisocyanate compound (Compound c) are charged first into a reactor in amounts in terms of an equivalent number ratio of hydroxyl groups:isocyanate groups of 1:1.5 to 2.5 and reacted in an organic solvent at a temperature of 80xc2x0 C. or below for 1 to 8 hours, and then the resulting isocyanate group-containing polybutadiene resin solution thus obtained is allowed to cool to room temperature, and then added with a tetrabasic acid dianhydride (Compound b) in an excessive amount over the isocyanate group, on the basis of the equivalent ratio, together with a reaction catalyst, and also with an additional organic solvent if necessary. The reaction mixture is kept at 120 to 150xc2x0 C. for 2 to 24 hours to carry out the reaction to the endpoint where all of the isocyanate groups have been reacted, or, alternatively, the reaction mixture is, for example dropwise, added with a diisocyanate compound and then kept at 120 to 150xc2x0 C. for 2 to 24 hours to effect polymerization to the endpoint where all of the isocyanate groups have been reacted, whereby obtaining an intended product. In the reaction described above, it is preferable that the acid anhydride equivalent number is equal to, or higher than, the isocyanate group equivalent number, and, at the same time, the isocyanate group equivalent number is equal to, or higher than, one-third of the acid anhydride equivalent number.
The organic solvent to be employed for the reaction described above can for example be a polar solvent such as N,Nxe2x80x2-dimethylformamide, N,Nxe2x80x2-diethylformamide, N,Nxe2x80x2-dimethylacetoamide, N,Nxe2x80x2-diethylacetoamide, dimethylsulfoxide, diethylsulfoxide, N-methyl-2-pyrrolidone, tetramethylurea, xcex3-butyrolactone, cyclohexanone, diglyme, triglyme, carbitol acetate, propylene glycol monomethylether acetate, propyleneglycol monoethylether acetate or the like. Such solvents can be employed alone or as a solvent mixture of two or more thereof. Any of these polar solvents can also be combined with a non-polar solvent such as aromatic hydrocarbons.
The reaction catalyst for the reaction described above can for example be a tertiary amine such as tetramethylbutane diamine, benzylmethylamine, triethanolamine, triethylamine, N,Nxe2x80x2-dimethylpyperidine, xcex1-methylbenzyldimethylamine, N-methylmorpholine, triethylenediamine or the like, and an organic metal catalyst such as dibutyltin laurate, dimethyltin dichloride, cobalt naphthenate, zinc naphthenate or the like, each of which can be used alone or two or more of which can be used in combination, with triethylenediamine being most preferred.
The modified polyimide resin-comprising resin composition of the present invention comprises, as the essential component, a polybutadiene polyol having a number average molecular weight of 1,000 to 8,000 and having 2 to 10 hydroxyl groups per molecule (Component A), a modified polyimide resin represented by Formula (4) shown above (Component B) and a polybutadiene polyblock isocyanate having a number average molecular weight of 1,000 to 8,000 and having 2 to 10 block isocyanate groups per molecule (Component C), wherein the weight ratio of Component A and Component B is preferably a (A):(B) ratio of 40:60 to 90:10 in terms of solid matter, and also wherein the amount in terms of equivalent number of said polyblock isocyanate is preferably 0.8 to 3.5 times the sum of the hydroxyl group equivalent number of Component A and the acid anhydride equivalent number of Component B.
A polybutadiene polyol having a number average molecular weight of 1,000 to 8,000 and having 2 to 10 hydroxyl groups per molecule (Component A) in the resin composition described above is important for providing both of the characteristics of rigid resins such as heat resistance, chemical resistance and the like and those of pliable resins such as flexibility, reduced shrinkage and the like. A molecular weight less than the range specified above or a number of the hydroxyl groups per molecule exceeding the range specified above causes a higher crosslinking density upon setting of a resin composition described above, which leads to a harder mass or article resulting in difficulties in obtaining satisfactory physical properties such as pliability of a hardened coat film and a reduced shrinkage upon setting. On the other hand, a molecular weight exceeding the range specified above or a number of the hydroxyl groups per molecule less than the range specified above causes a lower crosslinking density upon setting, which leads to a more pliable mass or article but also to a markedly reduced heat resistance or chemical resistance of a hardened coat film. In addition, since Component A has a polybutadiene backbone, the reduced shrinkage upon setting and the pliability of a hardened mass or article can further be increased.
Since a modified polyimide resin represented by Formula (4) in the resin composition described above has a reduced number of functional groups and a suitable molecular weight and also has pliability attributable to the butadiene backbone, it is important to impart the resin composition with a reduced shrinkage upon setting and also to impart a hardened coat film with pliability. In addition, since it also has an imide backbone which contributes to heat resistance and chemical resistance, it is important to achieve both of the pliability and the heat and chemical resistances, to some extent, at the same time. Furthermore, since this resin has polybutadiene units, it can form an extremely uniform mixture with a polybutadiene polyol having a number average molecular weight of 1,000 to 8,000 and having 2 to 10 hydroxyl groups per molecule (Component A) and a polybutadiene polyblock isocyanate having a number average molecular weight of 1,000 to 8,000 and having 2 to 10 block isocyanate groups per molecule (Component C), and can be incorporated characteristically firmly into the crosslinking system formed by Component A and Component C. Accordingly, the addition of Component B is further effective in obtaining pliability and reduced shrinkage upon setting while suppressing an adverse effect on excellent characteristics of the crosslinking system established by Component A and Component C such as heat resistance, chemical resistance, moisture resistance and the like.
A polybutadiene polyblock isocyanate having a number average molecular weight of 1,000 to 8,000 and having 2 to 10 block isocyanate groups per molecule (Component C) in the resin composition described above is important for providing both of the characteristics of rigid resins such as heat resistance, chemical resistance and the like and the characteristics of pliable resins such as flexibility, reduced shrinkage and the like. A molecular weight less than the range specified above or a number of the hydroxyl groups per molecule exceeding the range specified above causes a higher crosslinking density upon setting of a resin composition described above, which leads to a harder mass or article resulting in difficulties in obtaining satisfactory physical properties such as a reduced shrinkage upon setting and pliability of a hardened coat film. On the other hand, a molecular weight exceeding the range specified above or a number of the hydroxyl groups per molecule less than the range specified above causes a lower crosslinking density upon setting, which leads to a more pliable mass or article but also to a markedly reduced heat resistance or chemical resistance of a hardened coat film. In addition, since Component C has a polybutadiene backbone, the reduced shrinkage upon setting and the pliability of a hardened mass or article can further be improved.
When a polybutadiene polyol (Component A) alone is hardened with a polybutadiene polyisocyanate (Component C), the hardened mass or article becomes relatively well-balanced in terms of the heat and chemical resistance vs the reduced shrinkage upon setting and the pliability of the hardened mass or article. The reduced shrinkage upon setting and the pliability of the hardened mass or article are, however, still on insufficiently satisfactory levels, due to which the combination with a modified polyimide resin (Component B) is essential. Thus, mixed use at a ratio within the range represented by (A):(B)=40:60 to 90:10 is preferable, and an amount of a polyol (Component A) less than this range results in too a reduced crosslinking density, which leads to a marked reduction in the heat resistance or the chemical resistance of the coating formed. The amount in terms of equivalent number of the polybutadiene polyblock isocyanate (Component C) is 0.8 to 3.5 times the sum of the hydroxyl group equivalent number of Component A and the acid anhydride equivalent number of Component B, departing from which results in too a reduced crosslinking density, which leads to a marked reduction in the heat resistance, the chemical resistance or the like of the coat film formed.
The polybutadiene polyol (Component A) can be any one having a number average molecular weight of 1,000 to 8,000, having 2 to 10 hydroxyl groups per molecule and also having a butadiene backbone, and can for example be, but are not limited to, xe2x80x9cG-1000xe2x80x9d, xe2x80x9cGI-1000xe2x80x9d, and xe2x80x9cGQ-1000xe2x80x9d (all produced by NIPPON SODA) and xe2x80x9cR-45EPIxe2x80x9d (produced by IDEMITSU PETROCHEMICAL).
The polybutadiene polyblock isocyanate (Component C) is one obtainable by blocking an isocyanate group-containing polybutadiene polyisocyanate with a blocking agent. Such polybutadiene polyisocyanate can for example be one obtainable by reacting a diisocyanate such as toluene-2,4-diisocyanate, toluene-2,6-diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, diphenylmethane diisocyanate, isophorone diisocyanate or the like, or a derivative thereof which has been imparted with three functionalities or more by means of the cyclization trimerization reaction of isocyanate groups or by means of the reaction of a part of the isocyanate groups with various polyols, with a hydroxyl group-containing polybutadiene having a number average molecular weight of 600 to 7,000, and includes xe2x80x9cTP-1002xe2x80x9d (produced by NIPPON SODA) and xe2x80x9cHTP-9xe2x80x9d, xe2x80x9cHTP-5MLDxe2x80x9d, and xe2x80x9cUNIMAX Pxe2x80x9d (all produced by IDEMITSU PETROCHEMICAL) and the like. As the blocking agent, a compound which has only one active hydrogen, per molecule, capable of being reacted with an isocyanate group and is dissociated again at 170xc2x0 C. or higher even after being reacted with the isocyanate group, is preferred, including, but not limited to, xcex5-caprolactam, diethyl malonate, ethyl acetoacetate, acetoxime, methylethylketoxime, phenol, cresol and the like.
The resin composition comprising a modified polyimide resin of the present invention can also comprise, in addition to the essential components described above, various additives employed customarily in this field, such as a setting promoter for polyols and isocyanates, a filler, an auxiliary agent, a thixotropy-imparting agent, a solvent and the like. It is desirable to add rubber microparticles especially for the purpose of further improving folding resistance, while it is desirable to add polyamide microparticles for the purpose of obtaining a further closer contact with an underlying copper circuit, with a polyimide or polyester film base substrate, or with an adhesive layer.
The rubber microparticle can be any resin microparticle which has been made to be insoluble in an organic solvent, or to be unmeltable and is obtainable by subjecting a resin exhibiting a rubber elasticity such as acrylonitrile butadiene rubber, butadiene rubber and acrylic rubber to a chemical crosslinking treatment, including, but not limited to, xe2x80x9cXER-91xe2x80x9d (available from NIPPON SYNTETIC RUBBER), xe2x80x9cSTAPHILOID AC3355xe2x80x9d, xe2x80x9cSTAPHILOID AC3832xe2x80x9d, and xe2x80x9cIM101xe2x80x9d (all produced by TAKEDA CHEMICAL INDUSTRIESxe2x80x9d, xe2x80x9cPARALOID EXL2655xe2x80x9d, and xe2x80x9cPARALOID EXL2602xe2x80x9d (all produced by KUREHA) and the like.
The polyamide microparticle can be any microparticle having a particle size of 50 microns or less and made of a resin having amide bond(s), including an aliphatic polyamide such as nylon, an aromatic polyamide such as KEPLER and a polyamideimide, and can for example be, but is not limited to, xe2x80x9cVESTOSINT 2070xe2x80x9d (produced by DICEL-HUELS), xe2x80x9cSP500xe2x80x9d (produced by TORAY), and the like.